Fire and Emergency say the SkyCity convention centre fire is proving "very challenging" to extinguish and emergency services are yet to fully control the blaze.
Assistant area commander Dave Woon briefed the media in a conference on Nelson Street shortly after 3:20pm.
"We currently have a fire on the seventh floor, that has travelled down to the sixth floor," he said.
"We have a sixth alarm, which is a large number of resources - Auckland is at its capacity."
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Woon said all firefights are utilised in "internal fire attack".
"It is a large fire involving gas cylinders. It started around the roof, around the guttering area. There is bitumen [asphalt] and insulation on fire... about two layers of insulation which appears to be straw," he explained to reporters.
"It's a very difficult fire to extinguish... we are effectively working from the inside.
"It's a very challenging fire, we've been here for hours and we're not on top of it... but with the resources that have arrived, we should be able to make progress."
Woon said one person is still being accounted for, but emergency teams do not hold grave fears.
"We don't think that's a problem," he said.
St John have confirmed that one person has been taken to Auckland Hospital in a serious condition.
"We will know where we stand in an hour."
It is still not known what caused the blaze.